1. Field of the Invention
The present invention relates to a non-reciprocal circuit element, such as an isolator or a circulator, which can be applied to a transmitting unit of a mobile communication device, such as a cellular phone or the like.
2. Description of the Related Art
FIG. 12 is an exploded perspective view of a conventional non-reciprocal circuit element. Hereinafter, a configuration of the conventional non-reciprocal circuit element will be described with reference to FIG. 12. A first yoke 51 made of a boxlike magnetic plate (iron plate or the like) is boxlike and a magnet 52 having a rectangular shape is attached to the inside of the first yoke 51 by means of a magnetic force or the like.
A second yoke 53 made of a magnetic plate (iron plate or the like) has a lower plate 53a and two side plates 53b which are bent upward from two opposite sides of the lower plate 53a. The second yoke 53 is coupled with the first yoke 51 to form a magnetic closed circuit.
A boxlike resin case 54 made of a synthetic resin molding product has a circular through hole 54b provided at a central portion of a lower wall 54a and a plurality of concaves 54c with bottoms provided around the through hole 54b. In addition, the resin case 54 is assembled with the second yoke 53, so that the lower plate 53a is exposed to the outside through the through hole 54b. 
An output terminal 55 and a ground terminal 56 made of metal plates are buried in the resin case 54 to be attached thereto. In addition, the output terminal 55 protrudes toward a sidewall 54d in a state in which the output terminal 55 is arranged to be exposed onto the lower wall 54a and the ground terminal 56 protrudes toward the sidewall 54d in a state in which the ground terminal 56 is exposed onto an inner lower surface of the concave portion 54c. 
First to third capacitors C1, C2, and C3 are formed of chip type capacitors. While being located into the concave portions 54c of the resin case 54, the first to third capacitors C1, C2, and C3 have their lower electrodes (not shown) that are soldered to and mounted on the ground terminal 56 located on the inner lower surfaces of the concave portions 54c. Further, a chip type resistor R has one electrode (not shown) that is soldered to and mounted on the ground terminal 56.
A disk-shaped ferrite member 57 made of YIG (Yttrium iron garnet) or the like is inserted into the through hole 54b of the resin case 54 in a state in which the disk-shaped ferrite member 57 is located in the through-hole 54b of the resin case 54, and a lower surface of the ferrite member 57 is mounted on the lower plate 53a of the second yoke 53.
A flat plate-shaped dielectric 58 is composed of a laminated plate obtained by laminating a plurality of insulating thin plates, and first to third central conductors 59, 60, and 61 are disposed at different laminated locations of the dielectric 58 such that parts of them cross each other in a vertical direction.
In addition, the dielectric 58 is mounted on the ferrite member 57, and the first to third central conductors 59, 60, and 61 have port portions connected to upper electrodes of the first to third capacitors C1, C2 and C3 and the output terminal 55 and ground portions of the first to third capacitors C1, C2 and C3 are connected to the ground terminal 56 (for example, see Japanese Unexamined Patent Application Publication NO. 11-298207).
However, the conventional non-reciprocal circuit element need to have the ground terminal 56 buried in the resin case 54 in order to ground the resin case 54 by which the ferrite member 57 and the first to third capacitors C1, C2, and C3 are located and held, the lower electrodes of the capacitors C1, C2, and C3, and the ground portions of the first to third central conductors 59, 60 and 61, and the non-reciprocal circuit element has a large size and many components, which results in increase of cost. In addition, a molding work for burying the output terminal 55 and the ground terminal 56 into the resin case 54 and an assembling work of the second yoke 53 and the resin case 54 are troublesome. As a result, the productivity decreases and the cost increase.
In addition, each of the capacitors C1, C2, and C3 has a thickness thinner than that of the ferrite member 57. Therefore, in a state in which the concave portion 54c is lifted, the work for burying the output terminal 55 and the ground terminal 56 into the resin case 54 becomes necessary, so that a metal mold for forming the resin case 54 becomes complicated, thereby increasing the cost.
The conventional art has the following problems. Specifically, since the conventional non-reciprocal circuit element needs to have the ground terminal 56 buried in the resin case 54 in order to ground the resin case 54 by which the ferrite member 57 and the first to third capacitors C1, C2, and C3 are located and held, the lower electrodes of the capacitors C1, C2, and C3 and the ground portions of the first to third central conductors 59, 60 and 61, the non-reciprocal circuit element has a large size and many components, which results in an increase of the cost. In addition, a molding work for burying the output terminal 55 and the ground terminal 56 into the resin case 54 and an assembling work of the second yoke 53 and the resin case 54 are troublesome. As a result, the productivity decreases and the cost increases.
In addition, each of the capacitors C1, C2, and C3 has a thickness thinner than that of the ferrite member 57. Therefore, in a state in which the concave portion 54c is lifted, the work for burying the output terminal 55 and the ground terminal 56 into the resin case 54 becomes necessary, so that a metal mold for forming the resin case 54 becomes complicated, thereby increasing the cost.